Xerographic powder filter



May 24, 1966 R. w. BENSON s-rAL 3,252,274

XEROGRAPHI C POWDER FILTER Filed Aug. l, 1962 NS U OF- N .SK Dn @ANO O TET l NBS m ww/ mmm B m0 M P7 United States Patent O 3,252,274 t XEROGRAPHIC POWDER FHLTER Robert W. Benson, Rochester, and David R. Stokes, Fairport, NX., assignors to Xerox Corporation, Rochester, N.Y., a corporation of New York Filed Aug. 1, 1962, Ser. No. 213,942 1 Claim. (Cl. 55-377) This invention relates to xerography and, in particular, to an improvedfilter bag assembly for removing xerographic toner particles from air in the exhaust system of the plate-cleaning station of a xerographic machine.

In the process of xerography, for example, as disclosed in Carlson Patent 2,297,691, issued October 6, 1942, a xerographic plate, comprising a photoconductive'insulating material on a conductive backing, is given a uniform electric charge over its surface and is then exposed to the subject matter to be reproduced, usually by conventional projection techniques. This exposure discharges the plate areas in accordance with the light intensity which reaches them and thereby creates an electrostatic latent image on or in the plate coating.

Development of the electrostatic latent image is usually effected by an electrostatically attractable material, which is generally a thermoplastic resin in the form of finely divided particles usually in the size lrange from 3 to 2O microns, commonly referred to `as toner or toner powder. In the development of the electrostatic latent image, the toner powder is brought into surface contact with the coating and is held thereon electrostatically in a pattern corresponding to the electrostatic latent image. The developed image is then transferred to a suitable support material, such as paper, and fused thereon to make a permanent image. `In the xerographic transfer step substantially all of the resin material or toner is caused to adhere to the support material to form the images thereon, but usually a very small percentage ofthe resin material or toner remains on the xerographic plate.

The small quantity of resin material or toner remaining on the xerographic plate will affect future operating steps of the xerographic process and if left remaining thereon has an accumulative effect in that additional residual toner particles would adhere more readily to the xerographic drum in both image and non-image areas thereon.

As disclosed in the Turner et al. Patent 2,751,616, issued June 26, 1956, a rotating brush in peripheral contact with the surface of the xerographic plate may beused to clean the xerographic plate of any residual resin material or toner adhering thereon. The brush, in turn, may be cleaned by a flicking bar disclosed in the above-referenced patent and by a vacuum system similar in structure to that of the common household vacuum cleaner, whereby dust, that is, residual resin material orl toner, is entrained in air and then filtered out from the air by a suitable filter.

In conventional vacuum cleaners it has been common practice to filter dust particles from an air stream by means of disposable filter bags of the type disclosed in Meyerhoefer Patent 2,720,277, issued October l1, 1955, in which the filter bags are made of suitable air-pervious material, such as paper.

Paper filter bags of the type disclosed in the abovereferenced Meyerhoefer patent usually operate with a pressure differential of about 50 to 60 inches of water across `the surfaces of the filter bag. It is apparent that a rather high pressure type fan or blower is required to produce this large a pressure drop across the filter bag. A fan or blower of the type generally used in a vacuum cleaner usually operates at a relatively high speed with a resultant high noise level which to many people is objectionable.

It is also common practice to make filters out of loosely 3,252,274 Patented May 24, 1966 ICC assembled fibrous webs or mats of fiber glass since it is known that these loosely assembled fibrous webs or mats are very porous and that only a relatively small pressure differential is required to force air through a filter made of fiber glass. However, existing filters made of fiber glass are not self-supporting, per se, but instead they are usually formed as a liner within a suitable filter support made of, for example, perforated cardboard or sheet metal. In the usual filters made of fiber glass, the effective area of the filter is greatly reduced by these structural supporting elements.

-In copending application, Serial No. 37,966, filed Iune 22, 1960, now abandoned in the name of Robert F. Osborne and Patsy J. Pugliese, Ir., there is disclosed a selfsupporting lter `bag fabricated from fiber glass, which, although capable of filtering toner particles from air at the cleaning station of a xerographic reproducing apparatus; has a useful life of relatively short duration.

It is, therefore, anobject of this invention to provide an improved disposable filter bag capable of being ope-rated for an extended period of time at a pressure differential of one-half to two inches of water across the faces of the filter bag for filtering dust particles of the type contemplated herein. y

Another object of this invention is to provide a structurally-self-sustaining filter bag of a highly porous material which can be readily fabricated from commercially available glass fiber material.

These and other objects of the invention are obtained by means of a disposable filter bag formed from a fiat blank or blanks of fiber glass mat material of varying density.

For a better understanding of the invention as well as other objects and further features thereof, reference is had to the following detailed description of the invention to be read in connection with the accompanying drawings, wherein:

FIG. l is a diagrammatic view, partly in section, of

the cleaning station of a xerographic machine wherein a FIG. 5 is an enlarged sectional view taken along line 5 5 of FIG. 4; and,

FIG. 6 shows a fiat blank from which the filter bag is constructed.

Referring now to the drawings there is shown in FIG. 1 the plate-cleaning station of a xerographic machine, in which 10 generally designates a xerographic plate including a layer 11 of photoconductive insulating material on a conductive backing 12 formed in the shape of a drum, which is suitably journaled for rotation in the direction indicated by the arrow to cause the drum surface sequentially to pass a plurality of xerographic processing stations, including the plate-cleaning station shown, as is common in the xerographic art. The plate cleaning assembly, generally designated 13, comprises a rotatable brush 14 of such construction as to apply extremely light pressure to the photoconductive surface of the xerographic drum to dislodge any particles of toner that may adhere thereto. The brush 14, in turn, is cleaned by a flicking bar 15 that is mounted within the hood 16 to contact the ends of the brush bristles, as they rotate, to detach particles of toner adhering thereto. The hood 16 encompasses approximately three-fourths of the brush area and is used for containing the particles of toner removed from 3 the drum by the brush and by the fiicking bar from the brush.

An elongated exhaust duct 17 is arranged to cover a slot that extends transversely across the hood 16 to permit the removal of dust particles from the hood, the exhaust duct protruding into a filter box 18 that is attached to the hood 16. The motor-driven centrifugal blower 19 connected by conduit 20 to the filter box produces a fiow of air through the filter box, drawing air through areas surrounding the xerographic drum and the hood, the air entraining particles of toner removed from the xerographic drum by the brush and by the flicking bar from the brush. Toner particles are separated from the air as it passes through the filter box by the filter bag 25, described in detail hereinafter, attached to the exhaust duct 17 so that only clean air reaches the motor-driven centrifugal blower 1-9.

Referring now to FIGS. 2 to 5, inclusive, there is shown a preferred embodiment of a filter bag constructed in accordance with the invention, the filter bag being formed with an inner wall of glass wool fibers (fiber glass) loosely assembled into a web or mat of progressive density and an outer wall of loosely assembled glass wool fibers into a web or mat of substantially uniform density to form a self-sustaining structure. The filter bag is formed as a tubular body provided with suitable end closures, recognized as being similar to the familiar gable-type top enclosures used on milk cartons.

The filter bag 25 is similar in construction to the filter bag disclosed in the referenced copending Osborne et al. application, Serial No. 37,966-in that it is formed of ber glass. In this prior art filter bag, the walls of the filter bag were made of fiber glass loosely assembled into a web or mat of uniform density. This type filter bag, when used to filter toner particles from the plate-cleaning station in an automatic xerographic reproducing apparatus,

j had a maximum useful life of approximately 18 hours equivalent to the machine processing time required in making approximately 4,000 copies. The criterion by which the useful life of a filter bag, as used in a xerographic reproducing apparatus, will be described in detail hereinafter.

In accordance with the invention, the walls of the improved filter bag `are constructed whereby the dow of air, containing the particles of toner, travels through a filtering medium of progressively increasing density and then through a filtering medium of substantially uniform density, the filtering media being a loosely assembled web or mat of fiber glass.

A single mat of fiber glass having, in cross section, an area of progressive density and then an area of uniform density may be used in fabricating the filter bag or, as shown, the lter bag may be formed from two mats of fiber glass, a fiat blank 28 of fiber glass mat material of progressive density to form the inner walls of the filter bag and a fiat blank 30 of fiber glass mat material of substantially uniform density to form the outer wall of the filter bag, the denser side of the blank 28 being positioned adjacent the surface of blank 30.

Since, in the preferred, the filter bag 25 is fabricated from fiat blanks 28 and 30 of substantially uniform width and length and are folded in the same manner, only blank 30 is illustrated and described in detail, the inside of such blank being shown in FIGURE 6.

By means of an appropriate pattern of fold lines, shown for blank 30 in FIGURE 6, the blanks are divided into a plurality of panels and areas which are utilized for the walls and the closure parts of the filter bag when it is erected.

The central and major areas of the blank 30 become the outer body of the container and is defined by spacedapart, longitudinally fold lines 31 and 32 running in substantially parallel relation across the inside face of the blank. At right angles thereto and intersecting the fold lines 31 and 32 and at spaced intervals therealong, is a series of parallel transverse fold lines 33, 34 and 35 and combined fold-and-seam lines 36 and 37 which define in the central and major area of the blank, front panel 38, rear panel 39, bottom panel 40, and top panel 41.

Integrally with the front, rear, bottom, and top panels 38, 39, 40 and 41, respectively, in the blank but separated therefrom by the longitudinal fold lines 31 and 32 is a plurality of panel extensions which when folded and secured together, as described hereinafter, form gable-like end closures for the filter bag. These areas include longitudinal fold-and-seam lines 42 and 43 parallel to fold lines 31 and 32, and spaced between the latter and the top and bottom edges, respectively, of the blank.

For enclosing the ends of the filter bag, front panel 38 has connected therewith inclined end panels 44 and 45; rear panel 39 has connected therewith inclined end panels 46 and 47. Similarly, bottom panel 40 has connected therewith triangular end panels 48 and 49, and top panel 41 has connected therewith triangular end panels 51 and 52.

End panel 48 is defined in part by fold line 31 and by fold lines 53 and 54 which converge and intersect at foldand-seam line 42, defining one side each of triangular foldback panels 55 and 56, respectively, fianking end panel 44. In a similar fashion end panel 49 is defined by a portion of fold line 32 and converging fold lines 57 and 58 which also respectively form sides of triangular foldback panels 59 and 61; end panel 51 is defined by a portion of fold line 31 and converging fold lines 62 and 63 which also form sides of trinagular fold-back panels 64 and 65, respectively; and end panel 52 is defined by a portion of fold line 32 and converging fold lines 66 and 67 forming boundary 'lines of triangular fold-back panels 68 and 69, each of the fold-back panels fianking its respective end panel.

Prior to the final erection step in which the blank 30 of fiber glass is fabricatedwith blank 28 into filter bag 25, the front panel 38 is cut to form an inlet passage 71 therein. To enable the filter bag to be connected firmly to the exhaust duct 17 a pair of collars 72 and 73 made of a suitable, normally rigid and inexpensive material as, for instance, cardboard, are perforated to form through apertures 74 which encircle inlet passage 71 when the collars are secured to opposite faces of the front panel 38 as by staples 75. Collar 72 is also stapled, by one staple 76 in each corner, to blank 28 to encircle an inlet passage 71A formed therein, in a manner similar to inlet passage 71 in blank 30.

To transform the blanks 30 and 28 into the completed filter bag illustrated, the blanks are first folded upon themselves to form an open-ended tube with the top panel 41 and rear panel 39 of both blanks fastened together by suitable fastening means, such as staples 75, inserted through the material of the blanks along the full length of the fold-and-seam lines 36 and 37. The ends of the filter bag are then closed by in-folding the end panels and fold-back panels into a gable-like end closure secured as by staples along the fold-and-seam lines 42 and 43.

As is typical of any stapling or sewing operation, sufiicient space must be left remaining adjacent to the desired seam or fastening line to prevent the fasteners from tearing loose from the edge of the material. To provide sufiicient material adjacent to the staples to prevent them from tearing loose from the material, marginal panels 46a, 55a, 56a, 44a, 64a, 65a, 6512, 41a, 69a, 69b, 68a, 45a, 61a, 59a, 47a, 47b, 39a and 46h are formed by material between the fold-and-searn lines 42, 37, 43 and 36, and the four edges of the blank; the marginal panels being further defined by fold lines 33, 34 and 35, previously described, and by fold lines 76, 77, 78 and 79 intersecting the converging fold lines defining the fold-back panels. These marginal panels enable the staples to retain a suitable purchase in the material to compress the panels into sealing relationship with each other in areaswhere they are fastened together. Whether the seams of the filter bag are made by stapling, as shown, or by other means such as by sewing or gluing the panels together along the seam lines, the resulting seams should be formed t`o prevent the escape of aeriform fiuid from the bag through any portion of the bag along the seams. In the case of staples, an efiicient seam may be made by placing the staples close together or in overlapping position.

The filter bag 25 may be inserted in the plate-cleaning assembly 13, as shown in FIG. 1, by frictionally sliding the collars surrounding the inlet passage in the filter bag into position over the exhaust duct 17 of hood 16.

Since inlet passage 71 in the front panel 38 is smaller in size than the apertures 74 in collars 72 and 73, there is sufficient fiber glass mat material surrounding these apertures to form an effective gasket around the exhaust duct as the collars encircle the exhaust duct.

With an air duct or passage of a given area, it is apparent that a filter bag constructed of a fiber glass material as shown would have approximately six times the filtering area of a conventional fiat panel fiber glass filter.

Although only a mat or mats of loosely assembled fiber glass are used in fabricating the filter bag, there is provided a filter bag having sufficient rigidity to support itself independently of filter box 18, whereby the entire surface area of the bag is available to permit passage of air.

Since all of the panel elements of the filter bag function as filtering elements, a filter of relatively large filtering area for the cross-sectional area of an air duct or passage is provided in the filter box. Due to the relatively low pressure drop required across the filter, the centrifugal blower 19 is only required to produce sufficient vacuum pressure to entrain the toner particles in a relatively slowly moving stream of air.

A fiber glass mat material having a substantially uniform density of about three-quarters of a pound to one pound per cubic foot for blank 30 and a fiber glass mat material of progressive density for blank 28 is preferred for the fabrication of a filter bag to effectively filter dust particles in the size range of three to twenty microns from an air stream. The maximum density of the most dense cross-sectional area of blank 28 should be less than or equal to the density of blank 30. With the use of materials in the above-described density range, the pressure drop across the walls of the bag will be within the range of one-half to two inches of water.

Filter bags constructed in accordance with the invention have been fabricated from material listed as follows.

Blank 30:

. 6 Weight-8 to 10 grams per square foot Manufactured by Modiglass Incorporated, Bremen, Ohio.

Using as a standardvof measurement for the useful life of a filter bag, theperiod of machine operating time during which the ,pressure drop across the filtering medium of the bag increases from one inch of water, when the filtering medium is clean, to one and one-quarter inches of water, as toner particles become entrapped in the filtering medium, the life of a filter bag constructed in accordance with the invention is approximately sixty hours as compared to useful life of approximately eighteen hours for a filter bag of the type disclosed in the referenced copending Osborne et al. application, Serial No. 37,966.

Obviously, numerous changes in construction and rearrangement of the parts of the filter bag may be resorted to without departing from the spirit o'f the invention as defined by the claim.

What is claimed is:

A disposable, self-sustaining filter bag for use in a vacu-4 um system having an exhaust duct through which air entrained particles fiow,

said filter bag including wall means,

said wall means being comprised of an outer Wall of fiber glass material having a substantially uniform density of between three-quarters of a pound to one pound per cubic f oot and an inner wall of fiber glass material of progressive density, the maximum density of which is less than the density of said outer wall of fiber glass material, and the most dense portion of which is positioned adjacent said outer wall of fiber glass material,

said wall means secured together in a manner to form a substantially closed filter bag that may be compressed to a collapsed position or expanded to an operative position, with said outer wall being the outer wall for the bag,

said wall means including a front portion having an inlet opening therein the shape of said inlet opening conforming to the outer shape of the exhaust duct and of a size smaller than the exhaust duct,

a first collar fastened to the outside of said outer wall,

a second collar fastened to the inside of said outer wall,

each of said collars having an aperture therein larger than said inlet opening in said outer wall and of a size for frictionally engaging the exhaust duct,

said first collar and said second collar being positioned so that said apertures therein are substantially aligned with said inlet opening, and

Microlite Glass Wool, B Fiber Ultraflne No. 1001 Fiber Glass Blanket, B Fiber Thickness inch. Fiber diameter' .000148 to .000175 inch. Percent of binder 20 20;|=3%.

1 1b, per cubic foot `Tohns Manville, Libbey Owens tlnlrd Division, Defiance,

Density Manufactured by.

Missouri.

1 lb, per cubic foot. Gustin Manufacturing Company, Kansas City 5,

Blank 28: MODIGLASS-Part No. RFM-% Thickness-V2 inch Adhesive 13 to18% by weight Density-Progressive (References on following page) References Cited by the Examiner UNITED STATES PATENTS Anderson 53-367 Sosnowich 55-382 X Borkoski 55--367 Pryor 55-527 Meyerhoefer 55-376 Henning 55-487 X 8 Stevens et al 55-367 Humphrey 55-376 Cropley 55-376 Brace 55-373 X Cordell 55-376 Korn 55-382 Aitkenhead 55-487 X HARRY B. THORNTON, Primary Examiner.

Slayter 55-341 10 L. H. MCCARTER, D. TALBERT, Assistant Examiners. 

